A preparation method of rare earth oxide dispersion strengthened fine grain tungsten materials

ABSTRACT

This invention relates to a preparation method of rare earth oxide dispersion strengthened fee grain tungsten materials, the mass percent of the rare earth oxide is of  0.1 - 2 %, and the rest ingredient is W. Weigh soluble rare earth salt and tungstate, dissolve into water to made into  50 - 100  g/L of rare earth salt solution and  150 - 300  g/L of tungstate solution, respectively. Firstly, add trace alkali in rare earth salt solution to control pH in  7 - 8 , then add organic dispersant and stir to form evenly suspended R(OH) 3  particle colloid (R refers to rare earth element). Secondly pour the tungstate solution into the R(OH) 3 colloid, add trace acid to control pH in  6 - 7 , then add organic dispersant and stir to form tungstic acid micro particles, which wrap around the colloidal particles, forming coprecipitation coating particle colloid. Thirdly, the coprecipitation coating particle colloidal is spray-dried, forming tungsten and rare earth oxide compound precursor powder. Alter that, ultrafine or nanoscale tungsten powder with particle size of  50˜500  nm is obtained through a process of calcination subsequent with hydrogen thermal reduction. Finally, the tungsten powder is subjected to ordinary compression molding and then conventional high temperature sintering. The trace rare earth oxide dispersion strengthened high performance fine grain tungsten materials prepared by this invention, its density is close to full density ( 98.5 % or higher), its grain size is uniform and very fine (average in  5˜10  microns), and the rare earth oxides particles evenly distribute in tungsten intracrystalline or grain, boundary with particle size of  100˜500  nm.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to the PCT application Ser. No. PCT/CN2014/088882, filed on Oct. 20, 2014, the disclosure of which is expressly incorporated by reference herein in its entirety.

TECHNICAL FIELD

The invention relates to field of nanomaterials and powder metallurgy field, especially a preparation method of rare earth oxide dispersion strengthened fine grain tungsten materials by nano-composite technology.

TECHNICAL BACKGROUND

Tungsten has characteristics such as high melting point, high hardness, good high temperature strength, thermal conductivity, electrical conductivity, low thermal expansion coefficient low sputtering and plasma effect, does not react with H, low H⁺ retention, is a very important high temperature structural materials and functional materials and is widely used as a plasma facing material and divertor component material in the nuclear fusion field.

Among the tungsten materials which have been put into application, pure tungsten material is a widely used, typical high temperature materials. At present powder high purification and grain boundary purification method are used to produce sintered pure tungsten material, which is then strengthened through large deformation process, tungsten grain size is about 100 microns, the ductile to brittle transition temperature (DBTT) is about 300˜350□, the recrystallization temperature is of 1300˜1350□ and room temperature tensile strength is more than 500 MPa, high temperature tensile strength at 1000□ is about 400 MPa. However, this material exists defects such as coarse grain, fiber microstructure, high DBTT, low recrystallization temperature, high brittleness. Adding a second phase particle to refine tungsten grain and to dispersion strengthen pure tungsten is an important direction of the current development. According to this, in the 2010 Chinese patent “A kind of preparation method of nanometer oxide dispersion strengthened ultrafine grain tungsten-based composite” (Patent number: ZL201010250552.X), Zhou et al used tungsten powder, Y₂O₃ or Y, sintering additives Ti as raw materials, adopt mechanical alloying method to prepare superfine solid solution alloying powder,, and then using the method of spark plasma sintering (SPS) to prepare rare-earth yttrium oxide dispersion strengthened tungsten material its relative density is 96˜99%, tungsten grain size is about 3 μm or less, it has good mechanical properties and thermal shock resistance. In addition, Kim et al in the 2009 article “the Fabrication of high temperature oxides dispersion strengthened tungsten composites by spark plasma sintering process”, Munoz et al in 2011 article “La₂O₃-reinforced W and W-V alloys produced by hot isostatic pressing” has also used mechanical alloying method to prepare tungsten and rare earth oxide composite powder, and used SPS or hot pressing method to prepare oxide dispersion strengthened tungsten materials, the results show that adding trace rare earth tungsten oxide can refine grain and improve strength and heat load resistance. in the Chinese patent “A preparation method of nanometer yttrium oxide dispersion strengthened tungsten alloy” (Application number: 201310123415.3), Guo et al improved the earlier described preparation methods, yttrium nitrate was dissolved in alcohol and then mixed with ammonium tungstate (APT) by ball milling, hydrogen reduction after drying, and then mixed with 0.1˜1% Ni as sinter activator, finally tungsten material with oxide dispersion distribution can be produced from high temperature sintering, its density is 18.28˜19.2 g/cm³.

The above research fully shows that the advantages of rare earth oxides addition in refining tungsten grain and improve the mechanical properties and thermal shock performance. But there exist some problems in the preparation of above: using high-energy ball milling or mechanical alloying preparation powder is easy to produce heterogeneous component distribution and impurities, and SPS, hot-pressing sintering method is not suitable for the engineering of large scale preparation. And although Guo's method improve the oxide dispersion distribution uniformity in tungsten matrix, but Ni must be added as sinter activator, and Ni element in many fields, such as nuclear fusion, nuclear fission is forbidden to use, this will be greatly limit the application scope. This patent inventor in the former stage has applied for and received a Chinese invention patent “one kind of method of preparing ultrafine activated tungsten, powder (patent number: ZL201010049432.3)”, in this invention, the “sol spray crying—thermal reduction” technology was used to prepare ultrafine or nanometer activated tungsten powder, in which, any one or more trace activation elements such as Ni, Co, Fe was added. Compared with high-energy ball mill or mechanical alloying, powder composition produced by this invention distributes uniformly, and does not introduce impurity elements. But due to poor compatibility of tungsten and rare earth oxide on the surface of the particles, if sol spray drying method is directly used to prepare tungsten materials containing trace rare earth oxide, rare earth oxide particle dispersion strengthening effect for tungsten is very limited, leading to poor performance, so it is difficult to meet the application requirement of nuclear fusion.

Invention contest:

In order to solve the problems in the above method in the preparing high performance rare-earth oxide dispersion strengthened fine grain tungsten materials, the present invention adopts the heterogeneous precipitation—spray drying—calcining—thermal reduction—conventional sintering technology to prepare high performance rare-earth oxide dispersion strengthened fine grain tungsten materials, its density is close to full density (98.5% or higher), and the rare earth oxides particles evenly distribute in tungsten intracrystalline or grain boundary, its grain size is uniform and very fine (average in about 10 microns or less), with good room temperature and high temperature performance as well as high thermal loading shock resistance.

A rare earth oxide dispersion strengthened fine grain tungsten material its character is that includes: rare earth oxides referred to any one or more of Y₂O₃, La₂O₃, or in CeO₂, the mass percent of the rare earth oxide is of 0.1˜2%, and the rest ingredient is W.

The above mentioned rare earth oxide dispersion strengthened fine grain tungsten material its character is that includes the following steps:

(1) The-mass percent of the rare earth oxide is of 0.1˜2%, and the rest ingredient is W. Weigh soluble rare earth salt and tungstate, dissolve into water to made into 50˜100 g/L of rare earth salt solution and 150˜300 g/L of tungstate solution, respectively. Firstly, add trace alkali in rare earth salt solution to control pH in 7˜8, then add organic dispersant and stir to form evenly suspended R(OH)₃ particle colloid (R refers to rare earth element). Secondly, pour the tungstate solution into the R(OH)₃ colloid, add trace acid to control pH in 6˜7, then add organic dispersant and stir to form tungstic acid micro particles, which wrap around the colloidal particles, forming coprecipitation coating particle colloid. Thirdly, the coprecipitation coating particle colloidal is spray-dried at 350˜450□ forming tungsten and rare earth oxide compound precursor powder, which is then calcined at 300˜600□ for 1˜4 h. After deaggregation and sieving, the calcined powder is hydrogen reduced at 600˜850° C. for 2˜6 h, ultrafine or nanoscale tungsten powder with particle size of 50˜500 nm is obtained. Rare earth oxides referred to any one or more of Y₂O₂, La₂O₃, or in CeO₂;

(2) The ultrafine/nanoscale tungsten powder containing trace rare earth oxide prepared in step (1) is compression molded under 150˜300 MPa using mold pressing or cold isostatic pressing;

(3) The pressing molded compaction is subjected to regular high temperature sintering in high temperature sintering furnace, sintering temperature is 1800˜2000□, holding time 1˜5 h, then dense high-performance rare earth oxide homogeneous dispersion strengthened fine grain tungsten materials are obtained.

The described tungstate is ammonium metatungstate, ammonium paratungstate or ammonium tungstate.

The described rare earth salts are nitrate, oxalate, carbonate, chloride or sulfate of Y, La or Ce.

The described stirring speed is 1000˜5000 revolutions per minute.

The described spray drying nozzle rotating speed is 20000˜30000 revolutions per minute.

The described reaction dispersant are stearic acid, polyethylene glycol (PEG), area, N, N-dimethyl formamide, OP emulsifier, twain-20 or sodium dodecyl sulfate, the mass fraction of reaction dispersant is of 0.1˜1.5% of rare earth salt solution or tungstate solution.

The described acid is hydrochloric acid (HCl), nitric acid (HNO₃) or oxalic acid (H₂C₂O₄), the described alkali is sodium hydroxide (NaOH), potassium hydroxide (KOH), or aqueous ammonia (NH₃·H₂O).

The Invention compared with the existing methods of the preparation of tungsten oxide dispersion strengthened materials, its advantages are as follows:

1. Compared with the conventional high energy ball mill and mechanical alloying, adopt “heterogeneous precipitation—spray drying” adding rare earth oxide in tungsten matrix, heterogeneous precipitation improves the compatibility of tungsten and rare earth oxides particles surface, spray drying achieves the uniformity of composition, microstructure in powder and alloy, so rare earth elements in tungsten matrix distribute more uniform, and do not introduce impurities.

2. Compared with high energy ball mill and mechanical alloying, ultrafine tungsten composite powder containing trace rare earth oxides prepared by “heterogeneous precipitation—spray drying—calcining—hydrogen reduction” method has much higher sintering activity; The powder of this invention can reach more than 98.5% density sintered at 1800˜2000□ by conventional sintering, grain size for sintered body is about 5˜10 microns, and microstructure more evenly, excellent toughness at room temperature and high temperature.

3. The invention adopts the conventional sintering method preparation of rare earth oxide dispersion strengthened fine grain tungsten materials, the technological process is simple and suitable for engineering preparation.

Concrete implementation way:

The following examples further explains the invention, instead of limiting the invention.

IMPLEMENTATION EXAMPLE 1

In the preparation of W-0.1 wt %Y₂O₃ of Y₂O₃ dispersion strengthening fine grain tungsten materials, for example.

(1) First of all, according to the mass fraction of rare earth oxides, weigh and soluble rare earth salt and tungstate by quality proportion, namely take 1.02 g yttrium, nitrate, 411.27 g ammonium tungstate, respectively made into 50 g/L of rare earth salt solution and 150 g/L of tungsten salt solution.

(2) Slowly drop ammonia with 10wt % concentration into yttrium nitrate solution, adjusting the pH to 7.2, and add 0.2 g PEG400 as dispersant, under the action of ultrasonic vibration and electric blender mixing, the rare earth salt and alkali reaction to form homogeneous suspension Y(OH)₃ particle colloid; Then adding tungsten salt solution into the Y(OH)₃ gel slowly drop oxalic acid with 10 wt % concentration, adjusting the pH to 6.5, and add 2 g PEG400 as dispersant, under the action of ultrasonic vibration and electric blender mixing to form tungstate micro particles, which precipitate and coat around the Y(OH)₃ gel particles, eventually form colloidal coprecipitation coating particles.

(3) Thirdly, the coprecipitated coating particle colloidal is spray-dried at 360□, spray drying nozzle rotating speed is 20000 revolutions per minute, forming tungsten and rare earth oxide compound precursor powder,

(4) The precursor powder is then calcined at 350□ for 2 h. After desegregation and sieving, the calcined powder is hydrogen reduced at 780° C. for 4 h, ultrafine tungsten powder containing 0.1 wt % Y₂O₃ is obtained.

(5) The ultrafine tungsten powder containing trace rare earth oxide is compression molded using mold pressing. The pressing molded compaction is subjected to pre-sintering and then high temperature sintered at 1950□ for 2 h and W-0.1 wt %Y₂O₃ material is obtained, its density is above 99.2%, its microstructure is uniform and very fine, average grain size is less than 10 microns. This materials can bear 200 MW/m² high heat flux loading without surface crack appearing.

IMPLEMENTATION EXAMPLE 2

In the preparation of W-0.3 wt % La₂O₃ of La₂O₃ dispersion strengthening fine grain tungsten materials, for example.

(1) First of all, according to the mass fraction of rare earth oxides, weigh and soluble rare earth salt and tungstate by quality proportion, namely take 1.53 g lanthanum oxalate hydrate, 411.27 g ammonium tungstate, respectively made into 60 g/L of rare earth salt solution and 200 g/L of tungsten salt solution.

(2) Slowly drop NaOH with 10 wt % concentration into lanthanum oxalate hydrate solution, adjusting the pH to 7.3, and add 0.3 g N,N-dimethyl formamide as dispersant, under the action of ultrasonic vibration and electric blender mixing, the rare earth salt and alkali reaction to form homogeneous suspension La(OH)₃ particle colloid; Then adding tungsten salt solution into the La(OH)₃ gel slowly drop HCl with 10 wt % concentration, adjusting the pH to 6.8, and add 1.5 g PEG400 as dispersant, under the action of ultrasonic vibration and electric blender mixing to form tungstate micro particles, which precipitate and coat around the La(OH)₃ gel particles, eventually form colloidal coprecipitation coating particles.

(3) Thirdly, the coprecipitated coating particle colloidal is spray-dried at 400□, spray drying nozzle rotating speed is 20000 revolutions per minute, forming tungsten and rare earth lanthanum oxide compound precursor powder.

(4) The precursor powder is then calcined at 350□ for 2 h. After deaggregation and sieving, the calcined powder is hydrogen reduced at 780° C. for 4 h, ultrafine tungsten powder containing 0.3 wt % La₂O₃ is obtained.

(5) The ultrafine tungsten powder containing trace rare earth lanthanum oxide is compression molded using mold pressing. The pressing molded compaction is subjected to pre-sintering and then high temperature sintered at 1950□ for 2 h and W-0.3 wt % La₂O₃ material is obtained, its density is above 99.1%, its microstructure is uniform and very fine, average grain size is less than 8 microns. This materials can bear 200 MW/m² high heat flux loading without surface crack appearing.

IMPLEMENTATION EXAMPLE 3

In the preparation of W-0.5 wt % CeO₂ of CeO₂ dispersion strengthening fine grain tungsten-materials, for example.

(1) First of all according to the mass fraction of rare earth oxides, weigh and soluble rare earth salt and tungstate by quality proportion, namely take 2.1 g cerium carbonate, 409.6 g ammonium tungstate, respectively made into 70 g/L of rare earth salt solution and 220 g/L of tungsten salt solution.

(3) Slowly drop KOH with 10 wt % concentration into cerium carbonate solution, adjusting the pH to 7.5, and add 0.3 g PEG400 as dispersant, under the action of ultrasonic vibration and electric blender mixing, the rare earth salt and alkali reaction to form homogeneous suspension Ce(OH)₃ particle colloid: Then adding tungsten salt solution into the Ce(OH)₃ gel, slowly drop HNO₃ with 10 wt % concentration, adjusting the pH to 6.5, and add 2.3 g PEG400 as dispersant, under the action of ultrasonic vibration and electric blender mixing to form tungstate micro particles, which precipitate and coat around the Ce(OH)₃ gel particles, eventually form colloidal coprecipitation coating particles.

(3) Thirdly, the coprecipitated coating particle colloidal is spray-dried at 400□, spray drying nozzle rotating speed is 25000 revolutions per minute, forming tungsten and rare earth cerium oxide compound precursor powder.

(4) The precursor powder is then calcined at 400□ for 2 h. After deaggregation and sieving, the calcined powder is two-step hydrogen reduced at 600□ for 2 h subsequent with 800□ for 2 h, ultrafine tungsten powder containing 0.5 wt % CeO₂ is obtained.

(5) The ultrafine tungsten powder containing trace rare earth cerium oxide is compression molded using cold isostatic pressing. The pressing molded compaction is subjected to pre-sintering and then high temperature sintered at 1950□ for 4 h and W-0.5 wt % CeO₂ material is obtained, its density is above 99.3%, its microstructure is uniform and very fine, average grain size is less than 8 microns. This materials can bear 200 MW/m² high heat flux loading without surface crack appearing.

IMPLEMENTATION EXAMPLE 4

In the preparation of W-0.3 wt %Y₂O₃-0.3 wt % La₂O₃ dispersion strengthening fine grain tungsten materials, for example.

(1) First of all, according to the mass fraction of rare earth oxides, weigh, and soluble rare earth salt and tungstate by quality proportion, namely take 1.52 g yttrium nitrate, 2.18 g lanthanum chloride, 409.2 g ammonium tungstate, respectively made into 80 g/L of mixed rare earth salt solution and 250 g/L of tungsten salt solution.

(2) Slowly drop ammonia with 10 wt % concentration into yttrium nitrate and lanthanum chloride solution, adjusting the pH to 7.8, and add 0.4 g sodium dodecyl sulfate as dispersant, under the action of ultrasonic vibration and electric blender mixing, the rare earth salt, and alkali reaction to form homogeneous suspension Y(OH)₃+ La(OH)₃particle colloid: Then adding tungsten salt solution into the Y(OH)₃+ La(OH)₃ gel, slowly drop oxalic acid with 10 wt % concentration, adjusting the pH to 6.2, and add 3.0 g sodium dodecyl sulfate as dispersant, under the action of ultrasonic vibration and electric blender mixing to form tungstate micro particles, which precipitate and coat around the Y(OH)₃+ La(OH)₃ gel particles, eventually form colloidal coprecipitation coating particles.

(3) Thirdly, the coprecipitated coating particle colloidal is spray-dried at 450□, spray drying nozzle rotating speed is 25000 revolutions per minute, forming tungsten and rare earth yttrium and lanthanum oxide compound precursor powder.

(4) The precursor powder is then calcined at 400□ for 3 h. After disaggregation and sieving, the calcined powder is hydrogen reduced at 800□ for 3 h, ultrafine tungsten powder containing 0.3 wt % Y₂O₃+0.3 wt % La₂O₃ is obtained.

(5) The ultrafine tungsten powder containing trace rare earth yttrium and lanthanum oxide is compression molded using mold pressing. The pressing molded compaction is subjected to pre-sintering at 1000□ for 2 h and then high temperature sintered at 1920□ for 3 h and W-0.3 wt % Y₂ +3.0 wt % La₂O₃ material is obtained, its density is above 99.4%, its microstructure is uniform and very fine, average grain size is less than 6 microns. This materials can bear 300 MW/m² high heat flux loading without surface crack appearing.

IMPLEMENTATION EXAMPLE 5

In the preparation of W-0.3 wt %Y₂O₃-0.3 wt % La₂O₃-0.3 wt % CeO₂ dispersion strengthening fine grain tungsten materials, for example.

(1) First of all, according to the mass fraction of rare earth oxides, weigh and soluble rare earth salt and tungstate by quality proportion, namely take 1.85 g sulfuric acid yttrium, 0.8 g lanthanum nitrate, and 0.8 g cerium nitrate, 409 g ammonium tungstate, respectively made into 100 g/L of mixed rare earth salt solution and 300 g/L of tungsten salt solution.

(2) Slowly drop NaOH with 10 wt % concentration into mixed rare earth salt solution, adjusting the pH to 8.0, and add 0.5 g twain-20 as dispersant under the action of ultrasonic vibration and: electric blender mixing, the rare earth salt and alkali reaction to form homogeneous suspension Y(OH)₃+ La(OH)₃+Ce(OH)₃ particle colloid; Then adding tungsten salt solution into the Y(OH)₃+La(OH)₃+Ce(OH)₃ gel, slowly drop HCl with 10 wt % concentration, adjusting the pH to 6.0, and add 4.0 g twain-20 as dispersant, under the action of ultrasonic vibration and electric blender mixing to form tungstate micro particles, which precipitate and coat around the Y(OH)₃+ La(OH)₃+ Ce(OH)₃ gel particles, eventually form colloidal coprecipitation coating particles.

(3) Thirdly, the coprecipitated coating particle colloidal is spray-dried at 450□, spray drying nozzle rotating speed is 30000 revolutions per minute, forming tungsten and rare earth yttrium+lanthanum+cerium oxide compound precursor powder.

(4) The precursor powder is then calcined at 500□ for 3 h. After deaggregation and sieving, the calcined powder is two-step hydrogen reduced at 600□ for 2 h subsequent with 800□ for 4 h, ultrafine tungsten powder containing 0.3 wt % Y₂O₃-0.3 wt %La₂O₃0.3 wt %CeO₂ is obtained.

(5) The ultrafine tungsten powder containing trace rare earth yttrium and lanthanum oxide is compression molded using mold pressing. The pressing molded compaction is subjected to pre-sintering and then high temperature sintered at 1950□ for 4 h and W-0.3 wt %Y₂O₃-0.3 wt %La₂O₃-0.3 wt %CeO₂ material is obtained, its density is above 99.1%, its microstructure is uniform and very fine, average grain size is less than 5 microns. This materials can bear 300 MW/m² high heat flux loading without surface crack appearing. 

1. A preparation method for rare earth oxide dispersion strengthened fine grain tungsten material, its character is that includes the following steps: (1) The mass percent of the rare earth oxide is of 0.1˜2%, and the rest ingredient is W. Weigh soluble rare earth salt and tungstate, dissolve into water to made into 50˜100 g/L of rare earth salt solution and 150˜300 g/L of tungstate solution, respectively. Firstly, add trace alkali in rare earth salt solution to control pH in 7˜8, then add organic dispersant and stir to form evenly suspended R(OH)₃ particle colloid (R refers to rare earth element). Secondly, pour the tungstate solution into the R(OH)₃ colloid, add trace acid to control pH in 6˜7, then add organic dispersant and stir to form tungstic acid micro particles, which wrap around the colloidal particles, forming coprecipitation coating particle colloid. Thirdly, the coprecipitation coating particle colloidal is spray-dried at 350˜450□, forming tungsten and rare earth oxide compound precursor powder, which is then calcined at 300˜600□ for 1˜4 h. After deaggregatlon and sieving, the calcined powder is hydrogen reduced at 600˜850° C. for 2˜6 h, ultrafine or nanoscale tungsten powder with particle size of 50˜500 nm is obtained. Rare earth oxides referred to any one or more of Y₂O₃, La₂O₃, or in CeO₂; (2) The ultrafine/nanoscale tungsten powder containing trace rare earth oxide prepared in step (1) is compression molded under 150˜300 MPa using mold pressing or cold isostatic pressing; (3) The pressing molded compaction is subjected to regular high temperature sintering in high temperature sintering furnace, sintering temperature is 1800˜2000□, holding time 1˜5 h, then dense high-performance rare earth oxide homogeneous dispersion strengthened fine grain tungsten materials are obtained.
 2. According to the preparation method of rare earth oxide dispersion strengthened fine grain tungsten materials in claim 1, its character is: the described tungstate is ammonium metatungstate, ammonium paratungstate or ammonium tungstate.
 3. According to the preparation method of rare earth oxide dispersion strengthened fine grain tungsten materials in claim 1, its character is: the described rare earth salts are nitrate, oxalate, carbonate, chloride or sulfate of Y, La or Ce.
 4. According to the. preparation method of rare earth oxide dispersion strengthened fine grain tungsten materials in claim 1, its character is: the described stirring speed is 10001˜5000 revolutions per minute.
 5. According to the preparation method of rare earth oxide dispersion strengthened fine grain tungsten materials in claim 1, its character is: the described spray drying nozzle rotating speed is 20000˜30000 revolutions per minute.
 6. According to the preparation method of rare earth oxide dispersion strengthened tine grain tungsten materials in claim 1, its character is: the described reaction dispersant are stearic acid, polyethylene glycol (PEG), urea, N,N-dimethyl formamide, OP emulsifier, twain-20 or sodium dodecyl sulfate, the mass fraction of reaction dispersant is of 0.1˜1.5% of rare earth salt solution or tungstate solution.
 7. According to the preparation method of rare earth oxide dispersion strengthened fine grain tungsten materials in claim 1, its character is: to control pH in step (1), the described acid is hydrochloric acid (HCl), nitric acid (HNO₃) or oxalic acid (H2C2O4), the described alkali is sodium hydroxide (NaOH), potassium hydroxide (KOH) or aqueous ammonia (NH₃·H₂O). 